The Limbic System • • • • • • Broca’s Limbic Lobe MacLean’s Limbic System Papez circuit Today’s Limbic System Today’s Emotional Brain Amygdala. A/Prof. Pascal CARRIVE SOMS UNSW Australia • Today the word “limbic” is associated with emotion processing, eg, “limbic system” refers to the brain emotional system. • The concept of limbic system as an emotional system is the legacy of McLean (1950’s) who refined the circuit for emotion proposed by Papez (1930’s) and used the anatomical name “limbic” introduced by Broca (1870’s). • The limbic system has evolved to the point that it is not longer anatomically correct or relevant. It should be abandoned and replaced by “brain emotional system” or “emotional brain”. 1. Broca’s Limbic Lobe Cingulate gyrus 1870’s. Paul Broca • describes a “limbic” lobe • (limbic = border) • Cingulate gyrus • hippocampus • Broca thought that the limbic lobe was involved in the processing of olfaction Olfactory bulb Hippocampus 2. MacLean’s Limbic System 1950’s. Paul MacLean MacLean limbic system is Broca’s limbic lobe plus: • fornix • hypothalamus • anterior nucleus of the thalamus • septal area • parahippocampal g. • amygdala Cingulate g f Ant Hyp Hippocampus Septal area Parahippocampal g amygdala The core of the system is the circuit of Papez for the processing of emotion 3. Papez circuit Sensory experience Emotional experience (affect) Neocortex 1930s. James Papez • Papez circuit was based on neurological, histopathological and neuroanatomical observations Cingulate gyrus fornix Thalamus Thalamus (anterior n.) Hypothalamus Hippocampus Emotional expression Sensory stimulus • Papez proposed a circuit that transforms a sensory experience into an emotional response made of an: • emotional expression (behavioral, autonomic) • emotional experience (affect) 4. Today’s Limbic System Further additions to MacLean’s limbic system in the last 60 years : • orbitofrontal cortex • dorsomedial nucleus of the thalamus • accumbens nucleus Dorsomedial n. of thalamus Accumbens n Cingulate g DM Orbitofrontal Cortex However, Papez circuit has not been confirmed experimentally and MacLean’s concept of limbic system has gradually been abandoned f Ant Hyp Hippocampus Septal area Parahippocampal g amygdala The term limbic remains to refer to emotional function in a loose sense, but it is a source of confusion. 5. Today’s Emotional Brain Dorsomedial n. of thalamus Accumbens n Cingulate g DM Orbitofrontal Cortex Hyp • Papez circuit has not been confirmed • Hippocampus involved in declarative memory, not directly in emotion processing • Only the anterior part of the cingulate gyrus is involved in emotion • Amygdala is the master controller of the emotion system Septal area amygdala 6. Amygdala. location amygdala 6. Amygdala. Internal organization Nearly 27 subnuclei! Corticomedial nuclei Central nucleus Basolateral nuclei Corticomedial nuclei • receive olfactory input Basolateral nuclei 1. receive all other inputs 2. process the information 3. sends processed information to central nucleus or back to cortex Central nucleus • Is the main output nucleus to hypothalamus and brainstem olfactory input Outputs to hypothalamus, brainstem All other inputs All other outputs 6. Amygdala. Inputs Sensory experience Somatosensory and visceral sensory input Insular cortex Ant cingulate g S1,2 DM Thalamus Orbitofrontal Cortex Hyp Raw and processed sensory information reaches the amygdala from: • Thalamus • Primary somatosensory cortex • Insula • Anterior Cingulate g • Orbitofrontal cortex • Hypothalamus amygdala Somatosensory Visceral sensory 6. Amygdala. Inputs Visual and auditory Insular cortex Raw and processed visual information reaches the amygdala from: • Thalamus • visual cortex • Ant Cingulate • Orbitofrontal cortex Ant cingulate g DM Thalamus Orbitofrontal Cortex V1 Hyp V2,3 Visual stimulus amygdala • Same for auditory information (temporal lobe instead of occipital) Sensory experience 6. Amygdala. Inputs Olfactory stimulus Insular cortex Ant cingulate g DM Thalamus Orbitofrontal Cortex Raw and processed visual information reaches the amygdala from: • Olfactory bulb • Primary olfactory cortex • Orbitofrontal cortex Hyp Hippocampus Olfactory stimulus Primary olfactory cortex amygdala Sensory experience Others • Hippocampus and parahippocampal g. 6. Amygdala. Outputs Descending output to: Emotional experience? Insular cortex • Hypothalamus • Brainstem responsible for: Emotional expression Ant cingulate g Feedback output to: DM Thalamus Orbitofrontal Cortex Hyp Hippocampus V2,3 • • • • • • • Orbitofrontal cortex Ant Cingulate cortex Insular cortex Visual cortex Auditory cortex Primary olfactory cortex Thalamus feedback with affective valence for: Emotional experience? amygdala Emotional expression • Hippocampus 6. Amygdala. Outputs Basal ganglia loop • With accumbens nucleus, dorsomedial thalamus and orbitofrontal cortex. ventral pallidum Accumbens n • Accumbens nucleus receives dopamine input from VTA. Codes for rewards and contributes to affective dimension of emotions DM Orbitofrontal Cortex amygdala Ventral Tegmental area (dopamine) 6. Amygdala. Place in the emotional brain Emotional experience? Insular cortex • drives the expression of emotions via descending projections Ant cingulate g • contributes to the emotional experience via reciprocal connections with multimodal association areas and ventral striatum/pallidum loop DM Thalamus Orbitofrontal Cortex Hyp Hippocampus V2,3 Emotional Learning amygdala The amygdala: Emotional expression • It is also responsible for emotional learning (association between salient stimuli and aversive /appetitive stimuli) Suggested readings Goossens, L., Sunaert, S., Peeters, R., Griez, E. J. L., & Schruers, K. R. J. (2007). Amygdala hyperfunction in phobic fear normalizes after exposure. Biological Psychiatry, 62(10), 1119–1125. doi:10.1016/j.biopsych.2007.04.024 Ressler, K. J., & Mayberg, H. S. (2007). Targeting abnormal neural circuits in mood and anxiety disorders: from the laboratory to the clinic. Nature Neuroscience, 10(9), 1116–1124. doi:10.1038/nn1944 Blond, B. N., Fredericks, C. A., & Blumberg, H. P. (2012). Functional neuroanatomy of bipolar disorder: structure, function, and connectivity in an amygdala-anterior paralimbic neural system. Bipolar Disorders, 14(4), 340–355. doi:10.1111/j. 1399-5618.2012.01015. Roxo, M. R., Franceschini, P. R., Zubaran, C., Kleber, F. D., & Sander, J. W. (2011). The limbic system conception and its historical evolution. TheScientificWorldJournal, 11, 2428–2441. doi:10.1100/2011/157150
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